The Institute for Cancer Research, Fox Chase Cancer Center, intends to purchase a Phillips EM420 transmission electron microscope with scanning and transmission scanning capability. The microscope will be operated as part of an existing shared electron microscope facility and will replace a Siemens 101 Elmiscope. The facility supports the investigations of ten current users of electron microscopy among 41 occasional and potential users at the Fox Chase Cancer Center. All users have programs in basic biomedical research that are independently funded through active or pending peer reviewed research grants. These research programs employ a variety of techniques in microscopy including high resolution microscopy of embedded sections and negatively stained preparations by transmission EM, freeze fracture and freeze etching techniques for topological studies, low resolution studies of nucleic acid structure, and high resolution scanning of secondary electrons for the imaging of cell surfaces. The equipment selected will satisfactorily fulfill these needs and provide the capability for the development of more sophisticated techniques of specimen preparation, for a variety of modes of specimen imaging, and for computer assisted image analysis of EM data. Development of these new techniques will enhance the value of electron microscopy as an investigative tool at the Center.